As is known in the art, slow-wave structures having a periodic array of elements of electrically conductive material whose dimensions and/or distances between the elements are comparable or less than a wavelength of an electromagnetic wave growing inside or passing through the slow-wave structure, are used in many high-power slow-wave vacuum electronic devices, such as travelling-wave and backward-wave tubes, and multi-cavity magnetrons. One example of such an slow-wave structure is an anode slow-wave structure shown in FIGS. 1A and 1B having a periodic array of cavities and vanes of electrically conductive material dimensioned for operation at frequencies corresponding to microwave band (0.3 GHz-30 GHz) of electromagnetic spectrum; here, in this example, there are six elements (vanes) of electrically conductive material equally spaced about the circumference of the cylindrical anode every 60 degrees and therefore have a periodicity of sixty degrees.
As is also known in the art, an electromagnetic meta-material structure having periodic array of elements of electrically conductive material whose dimensions and/or distances between the elements are comparable or less than a wavelength of an electromagnetic wave growing inside or passing through the metamaterial structure is one type of a slow-wave structure.
There is a growing need for high-power slow-wave vacuum electronic devices utilizing different slow-wave structures for operation at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum. However, fabrication of these slow-wave structures for operation at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum requires very precise fabrication methods. This is because the physical dimensions of each single element of these slow-wave structure and/or the distances between the elements are comparable or even less that the wavelength of an electromagnetic wave growing inside or passing through these slow-wave structures, which might be as small as a fraction of a millimeter and even less in millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum.
Current technologies used to fabricate slow-wave structures for operation at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum include, as it is mentioned in an article entitled “Vacuum Electronic High Power Terahertz Sources” by Booske et al., IEEE Transactions on Terahaertz Science and Technology, Vol. 1, No. 1, September 2011, beginning at page 454, are: (i) LIGA (The German acronym LIGA (LIthographie, Galvanik, and Abformung) a process involving photolithography, electroforming and molding and combines the precision of photolithographic methods with the ability to electroform vacuum compatible, low loss materials such as copper to very fine feature sizes around removable, photoresist-based molding agents; (ii) Deep Reactive Ion Etching (DRIE) which is a highly anisotropic etching process for silicon or, more recently, SiC, that produces high vertical aspect ratios up to 50:1; (iii) Electrical Discharge Machining (EDM) methods which rely on a small plasma discharge between the electrode (wire or block) and the work-piece and are usually performed submerged in de-ionized water or dielectric oil with localized flow to flush out debris; (iv) Traditional Computer Numerical Control (CNC) machining; and (v) Laser Ablation which while able to produce very fine features with high precision, is very slow because the debris must be cleared out before more material can be ablated. However, these technologies are relatively costly, complex, and not always environmental friendly.
In accordance with the disclosure, a method is provided for fabrication of slow-wave structures for high-power slow-wave vacuum electronic devices. The method includes: loading a digital three dimensional model of a slow-wave structure in a memory of a 3D printer, the loaded digital three dimensional model having data therein representative of the slow-wave structure to be fabricated by the 3D printer, loading metal powder material into the 3D printer; and operating the 3D printer to fabricate the slow-wave structure according to the digital three dimensional model of the slow-wave structure loaded in a memory of the 3D printer.
In accordance with the disclosure, a method is provided for fabrication of electromagnetic meta-material structures. The method includes: loading a digital three dimensional model of an electromagnetic meta-material structure in a memory of a 3D printer, the loaded digital three dimensional model having data therein representative of the electromagnetic meta-material structure to be fabricated by the 3D printer, loading metal powder material into the 3D printer; and operating the 3D printer to fabricate the electromagnetic meta-material structure according to the digital three dimensional model of the electromagnetic meta-material structure loaded in a memory of the 3D printer.
In accordance with the disclosure, a method is provided comprising using a 3D printing process enabling fabrication of slow-wave structures, including electromagnetic meta-material structures, dimensioned to operate at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum.
The use of a 3D printing process enables rapid fabrication of prototypes of slow-wave structures, including electromagnetic meta-material structures, during design/simulation phases of the slow-wave structure, including electromagnetic meta-material structures, design process.
In one embodiment, an electromagnetic meta-material structure is a slow wave structure.
In one embodiment, a method is provided for fabrication of slow-wave structures for high-power slow-wave vacuum electronic devices operating at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum. The slow-wave structure has a periodic array of elements of electrically conductive material, each of such elements of electrically conductive material having predetermined dimensions, and such elements of electrically conductive material being spaced one from another a predetermined distance. The method includes: (a) loading a digital three dimensional model of a slow-wave structure in a memory of a 3D printer, the loaded digital three dimensional model having data therein representative of the slow-wave structure to be fabricated by the 3D printer, (b) loading metal powder material into the 3D printer (c) operating the 3D printer to deposit a layer of the metal powder material having a thickness at least ten times less than the lesser of the predetermined dimensions of each one of the elements of electrically conductive material and/or the predetermined distance between these elements of electrically conductive material; (d) melting the deposited layer of the metal powder material in accordance with the loaded three dimensional model of the slow-wave structure to transform the deposited layer of the metal powder material into a layer of melted metal shaped in accordance with the loaded three dimensional model of the slow-wave structure; (e) solidifying the layer of melted metal to transform it into a layer of solid metal shaped in accordance with the loaded three dimensional model of the slow-wave structure; and (f) repeating (c) through (e) to fabricate the slow-wave structure layer by layer in accordance with the loaded three dimensional model of the slow-wave structure.
In one embodiment, an electromagnetic meta-material structure is a slow-wave structure and the method provided for fabrication of slow-wave structures for high-power slow-wave vacuum electronic devices operating at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum is also applicable for fabrication of electromagnetic meta-material structures operating at frequencies corresponding to millimeter-wavelength and terahertz-frequency bands of electromagnetic spectrum.
In one embodiment, a slow-wave structure is provided having a periodic array of elements of electrically conductive material spaced one from another in both a plane and along a column disposed along a direction perpendicular to such plane.
In one embodiment, the slow-wave structure is a cylindrical structure wherein the elements of electrically conductive material are radially directed rod-like elements. The dimensions of the elements of electrically conductive material and spacing of the elements of electrically conductive material one from another is determined during design/simulation phases of the slow-wave structure design process.
In one embodiment, the thickness of the elements of electrically conductive material is λ0/M, where M is between 3.5 and 4.5, and where λ0 is the operating wavelength of an electromagnetic wave growing inside or passing through the slow wave structure.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.